Small, apolar aromatic groups, such as phenyl rings, are commonly included in the structures of fluorophores to impart hindered intramolecular rotations, leading to desirable solid-state luminescence properties. However, they are not normally considered to take part in through-space interactions that influence the fluorescent output. Here, we report on the photoluminescence properties of a series of phenyl-ring molecular rotors bearing three, five, six, and seven phenyl groups. The fluorescent emissions from two of the rotors are found to originate, not from the localized excited state as one might expect, but from unanticipated through-space aromatic-dimer states. We demonstrate that these relaxed dimer states can form as a result of intra- or intermolecular interactions across a range of environments in solution and solid samples, including conditions that promote aggregation-induced emission. Computational modeling also suggests that the formation of aromatic-dimer excited states may account for the photophysical properties of a previously reported luminogen. These results imply, therefore, that this is a general phenomenon that should be taken into account when designing and interpreting the fluorescent outputs of luminescent probes and optoelectronic devices based on fluorescent molecular rotors.

To integrate anion-π, cation-π, and ion pair-π interactions in catalysis, the fundamental challenge is to run reactions reliably on aromatic surfaces. Addressing a specific question concerning enolate addition to nitroolefins, this study elaborates on Leonard turns to tackle this problem in a general manner. Increasingly refined turns are constructed to position malonate half thioesters as close as possible on π-acidic surfaces. The resulting preorganization of reactive intermediates is shown to support the disfavored addition to enolate acceptors to an absolutely unexpected extent. This decisive impact on anion-π catalysis increases with the rigidity of the turns. The new, rigidified Leonard turns are most effective with weak anion-π interactions, whereas stronger interactions do not require such ideal substrate positioning to operate well. The stunning simplicity of the motif and its surprisingly strong relevance for function should render the introduced approach generally useful.

Here we provide experimental evidence for anion-π catalysis of enamine chemistry and for asymmetric anion-π catalysis. A proline for enamine formation on one side and a glutamic acid for nitronate protonation on the other side are placed to make the enamine addition to nitroolefins occur on the aromatic surface of π-acidic naphthalenediimides. With increasing π acidity of the formally trifunctional catalysts, rate and enantioselectivity of the reaction increase. Mismatched and more flexible controls reveal that the importance of rigidified, precisely sculpted architectures increases with increasing π acidity as well. The absolute configuration of stereogenic sulfoxide acceptors at the edge of the π-acidic surface has a profound influence on asymmetric anion-π catalysis and, if perfectly matched, affords the highest enantio- and diastereoselectivity.

We report a versatile and scalable synthesis of a water-dispersible modular star polymer platform with an enzyme-inspired hydrophobic interior. The cores of the stars can be functionalized at will, independently from the modification of the polymer structure. We explored the use of this material for the creation of a local hydrophobic solvent environment in water and for site isolation of incompatible catalytic entities.

Anion-π interactions have been introduced to catalysis only recently, and evidence for their significance is so far limited to one classical model reaction in enolate and enamine chemistry. In this report, asymmetric anion-π catalysis is achieved for the first time for a more demanding cascade process. The selected example affords six-membered carbocycles with five stereogenic centers in a single step from achiral and acyclic substrates. Rates, yields, turnover, diastereo- and enantioselectivity are comparable with conventional catalysts. Rates and stereoselectivity increase with the π-acidity of the new anion-π catalysts. Further support for operational anion-π interactions in catalysis is obtained from inhibition with nitrate. As part of the stereogenic cascade reaction, iminium chemistry and conjugate additions are added to the emerging repertoire of asymmetric anion-π catalysis.

Two broad classes (Scheme 1) of molecular recognition processes [1] can be defined [2] -namely, 1) homophilic recognition, which involves the interaction of structurally and electronically similar, if not identical, species, and 2) heterophilic recognition in which constitutionally different species come together as a result of stabilizing intermolecular noncovalent bonding interactions. Nowhere are these concepts more relevant than when considering donor-acceptor recognition processes [3] between p-electron-rich and p-electrondeficient species. These donor-acceptor recognition motifs have aided and abetted the template-directed synthesis [4] of mechanically interlocked molecules [5] (MIMs), which have been employed in molecular electronic devices [6] (MEDs) and integrated bulk systems, [7] as well as in current state-of-the-art solar-cell technologies. [8] Many of these donor and acceptor units are also capable [9] of undergoing reversible one-electron redox processes, leading to stable radical intermediates which engage [10] in homophilic radical-radical interactions as a result of dimerization-often referred to as pimerization [11] in the older literature. Recently, we have demonstrated [12] that these homophilic radical-radical interactions can be exploited in the template-directed synthesis [4] of MIMs, while other researchers have shown [13] that they can be used to fabricate organic solid-state semiconducting materials. There are very few examples of p-electronic organic molecules, however, which can exhibit both hetero-and homophilic recognition in a single redox state. This exceptional behavior, wherein the molecule can exhibit both recognition processes, analogous to that of a chameleon within its environment, is chameleonic in nature. These rare molecules have the potential to be incorporated into nanoscale architectures and functional building blocks for MIMs, [5] MEDs, [6] and other integrated devices. [7, 8] Herein, we report 1) the solid-state superstructure of the dimethyldiazaperopyrenium dication [14] (MP 2+ ) based Scheme 1. The chameleonic nature of MP 2+ allows for homophilic molecular recognition even as a dicationic species, as well as donoracceptor interactions with p-electron-rich compounds. These provide an example of heterophilic recognition, which has been harnessed in the template-directed synthesis of the [2]rotaxanes 1R 2+ and 2R 2+ in addition to the [3]rotaxane 3R 2+ .

In order to overcome the critical limitations of liquid electrolytebased dye-sensitized solar cells, quasi-solid-state electrolytes have been explored as a means of addressing long-term device stability, albeit with comparatively low ionic conductivities and device performances. Although metal oxide additives have been shown to augment ionic conductivity, their propensity to aggregate into large crystalline particles upon high-heat annealing hinders their full potential in quasi-solid-state electrolytes. In this work, sonochemical processing has been successfully applied to generate fine Co 3 O 4 nanoparticles that are highly dispersible in a PAN:P(VP-co-VAc) polymer blended gel electrolyte, even after calcination. An optimized nanocomposite gel polymer electrolyte containing 3 wt% sonicated Co 3 O 4 nanoparticles (PVVA-3) delivers the highest ionic conductivity (4.62 x 10-3 S cm-1) of the series. This property is accompanied by a 51% enhancement in the apparent diffusion coefficient of triiodide versus both unmodified and unsonicated electrolyte samples. The dye-sensitized solar cell based on PVVA-3 displays a power conversion efficiency of 6.46% under AM1.5G, 100 mW cm-2. By identifying the optimal loading of sonochemically processed nanoparticles, we are able to generate a homogenous extended particle network that effectively mobilizes redox active species through a highly amorphous host matrix. This effect is manifested in a selective 51% enhancement in photocurrent density (J SC = 16.2 mA cm-2) and a lowered barrier to N719 dye regeneration (R CT = 193 Ω) versus an unmodified solar cell. To the best of our knowledge, this work represents the highest known efficiency to-date for dye-sensitized solar cells based on a sonicated Co 3 O 4-modified gel polymer electrolyte. Sonochemical processing, when applied in this manner, has the potential to make meaningful contributions towards the ongoing mission to achieve the widespread exploitation of stable and low-cost dye-sensitized solar cells.

Acid-catalysed scrambling of the mechanically interlocked components between two different homo[3]rotaxanes, constituted of dumbbells containing two secondary dialkylammonium ion recognition sites encircled by two [24]crown-8 rings, each containing a couple of imine bonds, affords a statistical mixture of a hetero[3]rotaxane along with the two homo[3]rotaxanes, indicating that neither selectivity nor cooperativity is operating during the assembly process.